The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Known hybrid powertrain systems use torque machines employing one of two or more energy conversion processes to generate tractive torque, which may be used for vehicle propulsion. Known torque machines include internal combustion engines that convert fossil fuels to torque using combustion processes, and electric machines that convert stored electrical energy to torque using electro-magnetic processes. Other known torque machines may include, e.g., hydraulically powered torque machines and pneumatically powered torque machines.
Known hybrid powertrain systems use transmission devices to transfer torque between the torque machines and an output member connected to a driveline when the powertrain is applied to a vehicle. Known transmission devices employ differential gears and selectively activated torque transfer clutches to control and change speed ratios and to transfer torque between the torque machines and the output member. Known torque transfer clutches generally include hydraulically-activated wet clutches. The torque transfer clutches include multi-plate friction clutches that have parasitic spin losses caused in part by fluid that resists rotation of clutch elements when a clutch is deactivated. Hydraulic systems include hydraulic pumps and pressurized fluid transfer systems to transfer pressurized hydraulic fluid to activate the torque transfer clutches. Hydraulic systems also include valve bodies, which are bulky and difficult to manufacture. Known hydraulic pumps are mechanically-driven devices that use power originating from the engine. Known hybrid powertrain systems may use an electrically-powered hydraulic pump to provide supplemental hydraulic pressure when the engine is off during ongoing powertrain operation. It is known that hydraulic circuits and hydraulic clutch elements add weight to a powertrain system and consume power. Known one-way clutch devices have been applied to effect torque transfer in powertrain systems. Known powertrain systems include a control system to monitor various inputs from the vehicle and the operator and provide operational control of the powertrain. This may include controlling transmission operating state and gear shifting, controlling torque-generative devices, and regulating the power interchange among the energy storage device and the torque machines to manage outputs of the transmission, including torque and rotational speed.